1. Field of the Invention
The invention relates to a circuit arrangement which is suitable for an ultrasonic-presence-motion detector which has an ultrasonic transducer as a transmitting transducer and an ultrasonic transducer as a receiving transducer, and more particularly to such a circuit in which an oscillator produces an ac voltage for the transmitting transducer and a gate circuit is provided in order to chronologically control the feeding of wave forms of the ac voltage to the transmitting transducer, and a receiver circuit is provided which is connected to a receiving transducer and which obtains a received signal from the receiving transducer and feeds an evaluation circuit.
2. Description of the Prior Art
Ultrasonic motion detectors for non-contact opening and closing of a water faucet are well known in the art. In such detectors, the ultrasonic waves emitted by an ultrasonic transmitter impinge upon an object, for example, upon the hands situated beneath the opening of the faucet. The emitted ultrasonic radiation is reflected by the hands and a portion of this reflected radiation reaches an ultrasonic receiver transducer. The transducer produces a corresponding signal which is evaluated by an appertaining electronic circuit. The evaluation signal is then utilized for opening and closing an electro-magnetic valve.
It is of primary importance for warm water installations that a water faucet be operated by non-contacting operation, is not unnecessarily opened or remains open. Therefore, the ultrasonic detector device does not respond to a receptacle standing in the wash basin or to a cloth laid over the water faucet, and the operation takes place normally in the accordance with the principle of Doppler-frequency shifted ultrasonic detection.
This limitation with respect to moving objects, however, is not sufficient in itself, in that the water faucet understandably is not to respond to persons, for example, merely passing the wash basin, or to an opening door, situated in proximity to the wash basin. Measures are also to be taken that the ultrasonic detector device does not respond to the running water jet itself, as this would lead to a continuous opening of the water faucet.
There are already a number of suggestions in order to solve the previously-mentioned problems, which again individually have disadvantages, particularly with respect to an insufficient operating safety.